NASA's Earth Observing System (EOS) Program will place large unmanned polar-orbiting spacecraft in low-earth orbit to support a variety of earth-observation missions. The EOS AM instrument set has two instruments requiring Capillary Pumped Heat Transport Systems (CPHTS) using Capillary Pumped Loop (CPL) technology for thermal accommodation. Significant development testing is required to retire CPHTS design risks early in the EOS program. The first phase of CPHTS development testing has been completed using a modified version of an existing Martin Marietta test bed, the Technology Demonstration Model (TDM). The EOS/TDM testing provided additional proof-of-concept testing for CPL operations and pushed the performance envelope of the TDM system in order to determine the limits of CPL system performance. In addition, the testing provides a database from which analysis methods can be validated. This paper summarizes the EOS/TDM test results.